RE: Japanese Booster Boxes
Yeah, as others have said, Poly_100 is probably the best person for already-released BW Japanese cards; even with his high shipping costs, you get good, reliable service.
For new boxes (as in, BW8 and forward), I do take orders, as omahanime said. My prices are better than those of eBay, so contact me if you are still interested.
As for pull rates, the holo pull rate in BW series Japanese boxes is 1 holo for every 2 packs. So per box, there are generally 10 holo cards.
In terms of box contents, BW-series boxes contain 20 packs with 5 cards each, with the exception of Dragon Selection and Shiny Collection, which have 15 booster packs per box. Pre-BW series, boxes had 20 packs with 11 cards each. For the earliest sets (I believe Neo and before), boxes had 60 packs with 10 cards per pack, as Videoland stated above.
I definitely recommend collecting Japanese. The cards are of a better quality, and you get better pull rates. I have been collecting Japanese cards since DP, and have since backtracked to get mostly everything from VS series onwards.
Hope this helps.